Liquid infusion apparatus

ABSTRACT

A liquid infusion apparatus for fixing an outer cylinder of a syringe and a driver for pushing a plunger in a predetermined direction so as to exhaust liquid in the syringe, an incremental linear encoder arranged along the feeding axis of said driver for pushing the plunger, a detector of said incremental linear encoder mounted on a slider portion of the driver for pushing the plunger so as to generate a signal indicating a moving quantity of the plunger, and a sensor provided in the vicinity of a liquid exhaust port of the outer cylinder for setting along the feeding axis a remaining liquid quantity small section so as to generate a signal about a position of the plunger at the remaining liquid quantity small section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of Ser. No. 09/142,292filed on Sep. 3, 1998 and allowed on Aug. 10, 2000, now U.S. Pat. No.6,179,569, which is the National Stage of PCT/JP98/00064, filed Jan. 9,1998.

TECHNICAL FIELD

The present invention relates to a liquid infusion apparatus, and moreparticularly, relates to a liquid infusion apparatus having a drivingmeans for infusing liquid by pushing a plunger into a syringe.

BACKGROUND ART

FIG. 1 shows a conventional liquid infusion apparatus having a drivingmeans comprising a CPU 1, a motor driving circuit 2, a potentiometeroutput processing circuit 3, an encoder output processing circuit 4, amotor 5, gears 6, a feed screw 7, a carriage 8, a slider 9 (plungerpushing out portion), a rotary encoder 10, a potentiometer 13, a hook 11for operating the potentiometer 13, a wire 12, a syringe 14, and aplunger 15. In said conventional infusion apparatus shown in FIG. 1, thesyringe 14 having the plunger 15 therein is mounted stationarily. Thefeed screw 7 is arranged in parallel with said syringe 14, connected tothe motor 5 through the gears 6, and brought into engagement with thecarriage 8. The slider 9 is connected to the carriage 8 and brought intoengagement with an end of the plunger 15. The rotary encoder 10 isconnected to the motor 5 or the feed screw 7. The potentiometer 13 isarranged at a position in parallel with the feed screw 7. The hook 11 isconnected to an end of the wire 12 for rotating said potentiometer 13and arranged so as to engage with the carriage 8 when the carriage 8 ismoved to a remaining liquid quantity small section. The output of therotary encoder 10 is applied to the CPU 1 through the encoder outputprocessing circuit 4 and processed. The output of the potentiometer 13is applied to the CPU 1 through the potentiometer output processingcircuit 3 and processed. The motor is driven by a signal from the CPU 1through the motor driving circuit 2, so that the plunger 15 is pushedout at a predetermined speed through a predetermined length to exhaustthe liquid in syringe 14.

A further or second conventional liquid infusion apparatus shown in theJapanese Patent Application Laid-Open No. 42218/93 comprises a drivingmeans for driving a plunger of a syringe to move at a predeterminedspeed between a first and a second positions, and a first linear encoderarranged between a third and fourth positions corresponding to the firstand second positions, respectively, for detecting the absolute positionand the moving distance of said plunger. FIG. 2 shows the essentialportion thereof.

In the first conventional apparatus, no actual feeding quantity of thecarriage can be detected in case that a slip is generated about the feedscrew or the motor, or the carriage is floated on the feed screw, and noactual position of the remaining liquid quantity small section can bedetected in case that the wire is cut, or the contact of the electricterminal of the potentiometer is failure. Further, in the secondconventional apparatus, such problems that the actual feeding quantityof the carriage can not be detected because of the slip about the feedscrew or the motor, or of the floatation of the carriage on the feedscrew can be solved, because in the second conventional apparatus, themoving state of the carriage is detected by the linear encoder. However,the second conventional apparatus has such a problem that the linearencoder for detecting the absolute value is expensive and the skill isrequired. Accordingly, an object of the present invention is to providea liquid infusion apparatus having a driving means which can detectexactly and control the movement of the plunger so as to solve the aboveproblems.

Further, Japanese Patent Application Laid-Open No. 44390/88 discloses animproved liquid infusion apparatus comprising a feed screw to be drivenby a prime mover, and a slider movable linearly, wherein the slider isbrought into engagement with said feed screw so as to push out a plungerin a syringe and to exhaust liquid in the syringe, and a pressureexerted on the plunger by the slider is detected and compared with areference value to generate a warning signal.

In said liquid infusion apparatus, a pressure sensor is provided at aplunger pushing portion of the slider and an output of the sensor iscompared with a plurality of reference values so as to generate thewarning signal and to carry out safely the infusion. As shown in FIG. 3,however, in said liquid infusion apparatus an end of the plunger isbrought into contact simply with the slider, and accordingly in casethat the plunger is sucked into the syringe by an attractive force dueto the negative pressure applied to the syringe, the slider is broughtinto disengagement with the plunger, so that the liquid infusion cannotbe attained, but such state cannot be detected. Accordingly, the otherobject of the present invention is to provide a liquid infusionapparatus which can detect the negative pressure applied to the plunger.

FIGS. 4A and 4B are views explaining the operation of the otherconventional liquid infusion apparatus. FIG. 4A shows such a state thatthe syringe 14 and the plunger 15 are not yet mounted on the main bodyof the apparatus. FIG. 4B shows such a state that the syringe 14 and theplunger 15 are mounted on the main body. In FIGS. 4A and 4B, a referencenumeral 14-1 denotes a flange of the syringe 14, a reference numeral15-1 denotes a flange of the plunger 15. A reference numeral 16 denotesa slider, 16-1 denotes a holding member provided at the slider 16 forholding the flange 15-1 of the plunger 15, 16-2 denotes a pushingportion of the slider 16, 16-3 denotes a grooved portion formed on theholding member 16-1, and 17 denotes a lever of a slider unlock means(not shown). A reference numeral 17-1 denotes a push button of the lever17, 17-2 denotes a pivot shaft of the lever 17, 21 denotes a main bodyof the liquid infusion apparatus, and 21-1 denotes a groove provided atthe main body 21 for receiving therein the flange 14-1 of the syringe14. In order to install the syringe 14 and the plunger 15 to the mainbody 21 of the liquid infusion apparatus shown in FIG. 4A, the slider 16is disengaged from the feed screw 7 by pushing the pushing button 17-1of the lever 17, the slider 16 is moved toward the flange 15-1 of theplunger 15, and the pushing portion 16-2 is brought into contact with anouter end of the plunger 15, so that the syringe 14 and the plunger 15are fixed to the main body 21 as shown in FIG. 4B. The width of thegrooved portion 16-3 is determined corresponding to the maximumthickness of the flange 15-1 of the plunger 15.

In the above conventional apparatus, however, the width of the groovedportion 16-3 of the holding member 16-1 is fixed, and accordingly, ifthe thickness of the flange 15-1 of the plunger 15 is smaller than thatof the grooved portion, the plunger 15 cannot be held positively by theslider 16.

Further, in a liquid infusion apparatus wherein the liquid infusion iscarried out automatically by moving the plunger of the syringe using amotor, it is necessary absolutely to prevent the plunger from moving ina (suction) direction contrary to the pushing direction of the plunger.Accordingly, in the conventional liquid infusion apparatus, the rotarydirection of the motor is limited to only one direction by a motordriving program and an electric circuit thereof.

Recently, however, most of electric appliances generate many kinds ofelectric noises (electromagnetic waves) according to the development ofthe electronic systems, so that many problems of wrong operation due tothe noises have been encountered in the field of the medical services.

Further, Japanese Utility Model Application Laid-Open No. 89053/83discloses an improved liquid infusion apparatus comprising a feed screwdriven by a prime mover, and a slider movable linearly, engaged with thefeed screw so as to push out the plunger of the syringe and infuseliquid from the syringe, wherein the engagement and disengagement of theslider with the feed screw can be carried out corresponding to that ofthe slider with the syringe. In said conventional infusion apparatus, asshown in FIGS. 5A and 5B, a sliding means is provided at a driving pawlwhich is fitted into a driving member when the syringe is installed onthe main body, so that a feed screw is disengaged from a half-nut fixedto said driving member at the same time of the sliding of the drivingpawl. Japanese Patent Application Laid-Open No. 247347/91 discloses afurther conventional liquid infusion apparatus as shown in FIG. 6. Inthis apparatus, a movable block is provided movably reciprocally in anaxial direction of a syringe and connected to a driving means, and apushing portion of a plunger is provided at the movable block movablyreciprocally between a position where the pushing portion is engagedwith the plunger and a position where the pushing portion is disengagedfrom the plunger, and a half-nut is engaged with and disengaged from afeed screw according to the movement of the movable block.

The apparatus shown in FIGS. 5A and 5B, or shown in FIG. 6 has suchproblems that in the loading state the half-nut is floated on the feedscrew, because the half-nut is normally urged to the feed screw by aspring, so that the precise feeding operation cannot be carried out.Further, in the conventional apparatus, operations for engaging theplunger with the slider and for disengaging the plunger from the sliderare carried out at the same time with operations for engaging the feedscrew with the half-nut and for disengaging the feed screw from thehalf-nut. However, only a simple groove is provided at a holding portionof the slider for holding a flange of the plunger, so that the flange ofthe plunger is held unsteadily by the holding member due to thedifference between the thickness of the flange of the plunger and thewidth of groove formed on the holding portion of the slider, which aregenerated by the mechanical precision. In the conventional apparatusmentioned above, it is preferable generally to shape the feed screw soas to have teeth of rectangular in cross section, which is in parallelwith a vertical plane normal to the feeding direction of the feed screw,in order to prevent the half-nut from floating from the feed screw incase of loading. However, there are two problems. One problem is thatthe feed screw having teeth of the rectangular cross section is high inmanufacturing cost, because the manufacturing steps thereof are limited.The other problem is that the flange of the plunger cannot be heldprecisely by the holding member, because a gap is formed between theflange of the plunger and the groove of the holding member due to themanufacturing precision.

The task of the present invention is to solve the above problems and toprovide a liquid infusion apparatus of high precision and inexpensive.

DISCLOSURE OF THE INVENTION

A liquid infusion apparatus according to the present invention has meansfor fixing an outer cylinder of a syringe and driving means for pushinga plunger in a predetermined direction so as to exhaust liquid in thesyringe, and is characterized by comprising an incremental linearencoder arranged along the feeding axis of said driving means forpushing the plunger, detecting means of said incremental linear encodermounted on a slider portion of said driving means for pushing theplunger, means for processing an output of said detecting means,applying to an UP/DOWN counter and comparing with an initial valueinputted previously so as to generate a signal indicating a movingquantity of said plunger, and a sensor provided in the vicinity of anend of said outer cylinder for setting along said feeding axis aremaining liquid quantity small section, wherein said counter is resetor the counted value is memorized and then the counting is started by anoutput of said sensor so as to determine a position of the plunger atsaid remaining liquid quantity small section. According to the aboveconstruction, the moving quantity and the position of the carriage formoving the plunger can be detected directly by an inexpensiveincremental linear encoder. Further, the absolute position at theremaining infusion liquid quantity small section can be recognized innon-contact manner by counting feedback pulses from the encoder afterthat the carriage is passed across the detecting sensor for detectingthe starting point of the remaining infusion liquid quantity smallsection.

In a liquid infusion apparatus according to the present invention, aholding arm for holding a flange of a plunger is provided rotatably andmovably in a movable direction of a slider so as to push the flange ofthe plunger to the slider by the holding arm for holding.

According to the liquid infusion apparatus as mention above, the flangeof the plunger can be held precisely by the slider, even if the size ofthe syringe is varied, because the flange of the plunger is pushed tothe slider by the holding arm for holding.

Further, a liquid infusion apparatus of the present invention has aholding arm for pushing the flange of said plunger in a directionreverse to a pushing direction of the plunger toward a plunger holdingportion of said slider for holding, a pressure sensor provided at saidplunger holding portion of the slider, and a processing circuit forcomparing an output of said pressure sensor with a plurality ofreference values to generate a processing signal.

In said liquid infusion apparatus, even if a force stronger than apressure acting on the plunger by the slider is applied to the plungerso that the plunger is to be sucked into the syringe (negative pressurestate), the plunger can be held by the slider, and a negative pressurestate can be detected by comparing an output of said pressure sensor incase that the flange of said plunger is held by the plunger holdingportion by the holding arm with the reference values.

Further, a liquid infusion apparatus according to the present inventionhas a feed screw driven by a prime mover and a slider movable linearlyand engaged with said feed screw so as to push a plunger of a syringefor exhausting liquid in the syringe, and is characterized by comprisinga lever supported rotatably freely by a first shaft arrangedhorizontally and normally to a moving direction of said slider, a pushbutton provided at one end of said lever so as to project from saidslider, a slider releasing device, an interlocking rod interlocking withsaid slider releasing device, the other end of said lever beingcontacted with said interlocking rod, holding means supported by saidslider rotatably by a second shaft, which is in parallel to said firstshaft for press holding the flange of the plunger by the slider, aspring for urging the holding means to rotate in the clockwisedirection, and interlocking means for interlocking said holding meanswith said lever.

In the above construction, the flange of the plunger can be heldpositively by the slider, even if the size of the thickness of theflange of the plunger is varied, because the flange of the plunger ispushed to the slider by the holding arm for holding.

Further, a liquid infusion apparatus of the present invention ischaracterized by comprising a half-nut releasing device interlockingwith a releasing lever mounted on the slider, said half-nut releasingdevice comprising means for engaging the feed screw with the half-nutand disengaging the feed screw from the half-nut moved by a releasingcam having a step portion, and means for pushing the flange of theplunger to the slider by the holding arm for holding. Further, the crosssection of the tooth of the feed screw is inclined to a plane normal tothe feeding direction of the screw, so that the feed screw can bemanufactured by the form rolling process etc. in mass production basis.

In the above construction, the releasing cam of the half-nut releasingdevice is moved in the forward direction of the interlocking rod to urgethe half-nut to the feed screw, so that the releasing cam receives acomponent force in the vertical direction of a force applied to thehalf-nut on loading, thereby causing the half-nut is prevented fromfloating.

Further, the flange of the plunger is pushed to the slider by the armprovided at the slider, the flange is held positively by the slider andno gap is formed between the contact portion of the slider and the endof the plunger, so that the movements of the slider and the plungercoincide perfectly with each other and precise liquid infusion can berealized.

Further, a liquid infusion apparatus according to the present inventionhas a feed screw driven by a prime mover and a slider movable linearlyand engaged with said feed screw so as to push a plunger of a syringefor exhausting liquid in the syringe, and is characterized in that meansfor transmitting a driving force only in a syringe pushing direction isinserted between the feed screw and the prime mover.

In the liquid infusion apparatus according to the present invention, amechanical backstop is provided between a rotary shaft of the electricmotor and the feed screw, so that even if the electric motor is rotatedreversely by the external noise the feed screw is prevented fromrotating reversely, and the danger of the malfunction can be avoided.

The other objects and features of the present invention will becomeapparent from the following descriptions in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of the construction of aconventional liquid infusion apparatus;

FIG. 2 illustrates a schematic view of the construction of a linearencoder of the conventional liquid infusion apparatus;

FIG. 3 illustrates a view of an essential portion of a pressure sensoron a slider mounting portion in the conventional liquid infusionapparatus;

FIG. 4A illustrates a side view of an essential portion in a state thatan end of a plunger is not yet held by the slider of the conventionalliquid infusion apparatus;

FIG. 4B illustrates a vertical sectional side view of an essentialportion in a state that the end of the plunger is held by the slider ofthe conventional liquid infusion apparatus;

FIG. 5A illustrates a view of the conventional liquid infusionapparatus;

FIG. 5B illustrates a side view of the liquid infusion apparatus shownin FIG. 5A;

FIG. 6 illustrates a view of the conventional liquid infusion apparatus;

FIG. 7 illustrates a schematic view of a liquid infusion apparatusaccording to the present invention;

FIG. 8A illustrates a schematic view of a slit plate of an incrementalencoder for use in a liquid infusion apparatus according to the presentinvention;

FIG. 8B illustrates a view of the incremental encoder according to thepresent invention using the slit plate shown in FIG. 8A;

FIG. 8C illustrates a view of the incremental encoder according to thepresent invention using a reflecting plate;

FIG. 9A illustrates a side view of an essential portion in a state thatthe end of the plunger is not yet held by the slider of a liquidinfusion apparatus according to an embodiment of the present invention;

FIG. 9B illustrates a view, taken along lines A-A′ of FIG. 9A.;

FIG. 10A illustrates a side view of an essential portion in a state thatthe end of the plunger is held by the slider of the liquid infusionapparatus according to an embodiment of the present invention;

FIG. 10B illustrates a view, taken along lines A-A′ of FIG. 10A;

FIG. 11A illustrates a vertical sectional side view of an essentialportion of the slider of a liquid infusion apparatus according to anembodiment of the present invention;

FIG. 11B illustrates a vertical sectional side view of an essentialportion of the slider of a liquid infusion apparatus according to anembodiment of the present invention;

FIG. 11C illustrates a vertical sectional side view of an essentialportion of the slider of a liquid infusion apparatus according to anembodiment of the present invention;

FIG. 12A illustrates a sectional view of an essential portion of theslider of a liquid infusion apparatus according to another embodiment ofthe present invention;

FIG. 12B illustrates a sectional view of an essential portion of theslider of a liquid infusion apparatus according to another embodiment ofthe present invention;

FIG. 12C illustrates a sectional view of an essential portion of theslider of a liquid infusion apparatus according to another embodiment ofthe present invention;

FIG. 13 illustrates a diagram showing a property of a pressure sensor ofthe liquid infusion apparatus according to another embodiment of thepresent invention;

FIG. 14A illustrates a view of an essential portion in a state that theend of the plunger is not yet held by the slider of a liquid infusionapparatus according to another embodiment of the present invention;

FIG. 14B illustrates a view, taken along lines A-A′ of FIG. 14A.;

FIG. 15A illustrates a view of an essential portion in a state that theend of the plunger is held by the slider of a liquid infusion apparatusaccording to another embodiment of the present invention;

FIG. 15B illustrates a view, taken along lines A-A′ of FIG. 15A;

FIG. 16A illustrates a sectional view of an essential portion in a statethat the end of the plunger is held by the slider of a liquid infusionapparatus according to another embodiment of the present invention;

FIG. 16B illustrates a view, taken along lines A-A′ of FIG. 16A;

FIG. 17A illustrates a sectional view of an essential portion in a statethat the end of the plunger is not yet held by the slider of the liquidinfusion apparatus according to the embodiment shown in FIGS. 16A and16B;

FIG. 17B illustrates a sectional view, taken along lines A-A′ of FIG.17A;

FIG. 18A illustrates a sectional view of an essential portion in a statethat the end of the plunger is not yet held by the slider of a liquidinfusion apparatus according to another embodiment of the presentinvention;

FIG. 18B illustrates a view, taken along lines A-A′ of FIG. 18A;

FIG. 19A illustrates a sectional view of an essential portion in a statethat the end of the plunger is held by the slider of the liquid infusionapparatus according to the embodiment shown in FIGS. 18A and 18B;

FIG. 19B illustrates a view, taken along lines A-A′ of FIG. 19A;

FIG. 20A illustrates a sectional view of an essential portion in a statethat the end of the plunger is not yet held by the slider of a liquidinfusion apparatus according to another embodiment of the presentinvention;

FIG. 20B illustrates a view, taken along lines A-A′ of FIG. 20A;

FIG. 21A illustrates a sectional view of an essential portion in a statethat the end of the plunger is held by the slider of the liquid infusionapparatus according to the embodiment shown in FIGS. 20A and 20B;

FIG. 21B illustrates a view, taken along lines A-A′ of FIG. 21A;

FIG. 22 illustrates a side view showing a liquid infusion apparatusaccording to the other embodiment of the present invention; and

FIG. 23 illustrates a section view of a one-way clutch for use in theliquid infusion apparatus according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be explained with reference to thedrawings. FIG. 7 is a schematic view of a liquid infusion apparatusaccording to the present invention. Parts of the apparatus which aresimilar to corresponding parts of the conventional apparatus shown inFIG. 1 have been given corresponding reference numerals and need not befurther redescribed. As shown in FIG. 7, a plate 22 of a linear encoderis provided in parallel with a feeding screw 7, and a photo-coupler 23of a carriage 8 is provided so as to face to said plate 22. A sensor 24is provided in the vicinity of an end of said plate 22 corresponding toan end of a syringe 14. A dog 26 is provided on said carriage 8 so as toactuate said sensor 24. An output of said photo-coupler 23 is applied toa CPU 1 through an encoder output processing circuit 4, and an output ofsaid sensor 24 is applied to the CPU 1 through a sensor outputprocessing circuit 25.

As shown in FIG. 7, an incremental linear encoder is composed of theplate 22 arranged in parallel with the feeding screw 7, and thephoto-coupler 23 fixed to the carriage 8, which is stationarily engagedwith a slider 9. Further, the dog 26 for a remaining liquid quantitysmall section is mounted on the carriage 8, and the sensor 24 for theremaining liquid quantity small section is actuated by the movement ofthe carriage 8.

In operation, a pulse signal generated between the plate 22 with slitsand the photo-coupler 23 mounted on the carriage 8 is processed in theencoder output processing circuit 4 and applied to the CPU 1 as aninformation to show the movement of the carriage 8, so that the movementof the carriage 8 can be monitored directly.

Furthermore, a signal generated when the dog 26 mounted on the carriage8 is moved across the sensor 24 is processed by the sensor outputprocessing circuit 25 and applied to the CPU 1 as an information ofposition. Then an encoder feedback pulse obtained by processing thepulse signal generated from the photo-coupler 23 by the encoder outputprocessing circuit 4 is applied to an UP/DOWN counter and compared withan initial value applied to the UP/DOWN counter previously to recognizein non-contact manner an absolute position of the plunger at theremaining liquid quantity small section.

As shown in FIGS. 8A and 8B, an example of an optical incremental linearencoder for use in the liquid infusion apparatus according to thepresent invention comprises an opaque planar plate 22 having fine slits22-1 equidistantly apart from one another, and a photo-coupler 22-2consisting of a light emitting element 22-3 and a light receivingelement 22-4, wherein a pulse signal is obtained when the slit 22-1 ofthe plate 22 is moved across the optical axis of said photo-coupler22-2. As shown in FIG. 8C, an optical incremental linear encoder of theother embodiment of the present invention comprises the plate 22 withthe slits, a light reflecting plate 22-5 arranged in the vicinity of andin parallel with said plate 22, and a photo-coupler 22-6 consisting of alight emitting element 22-7 and a light receiving element 22-8 arrangedat the opposite side of the light reflecting plate 22-5 with respect tothe plate 22, wherein a pulse signal can be obtained corresponding to areflected light reflected from the light reflecting plate 22-5 throughthe slit 22-1 of the plate 22. Both optical incremental linear encodersare the same in function with each other and can be used similarly.

As stated above, the incremental linear encoder having the opaque planarplate having the fine slits equidistantly apart from one another for usein the liquid infusion apparatus of the present invention is simple inconstruction and low in manufacturing cost compared with theconventional absolute value type linear encoder shown in FIG. 2, whereina plurality of transparent sections of which width is narrower inconsecutive order are formed on both of the transparent andnon-transparent portions. The incremental encoder of the presentinvention has such features that the plate with slits can bemanufactured low in cost and that a high precision detecting signals ofthe moving speed, the moving distance and the absolute position etc. ofthe plunger can be obtained economically by processing and convertingthe output by a processing circuit.

In place of the optical type incremental linear encoder shown in FIG. 8,a magnetic type incremental linear encoder wherein a magnetic scaleplate having N poles and S poles formed alternately with a constantpitch is arranged at a position of the slit plate, and a magneticdetection device is arranged at a position of the photo sensor, can beused.

According to the liquid infusion apparatus having the above structure ofthe present invention, the detection's of the moving distance of theplunger and the absolute position of the plunger at the liquid remainingarea can be realized in non-contact manner by detecting the actualmotion of the carriage for pushing out the plunger.

Another embodiment of the present invention will now be explained withreference to FIGS. 9-11. FIGS. 9A and 9B show a state that the flange ofthe plunger in the syringe is not yet held by the slider portion. FIG.9A is a side view of the essential portion of the apparatus according tothe present invention, and FIG. 9B is a front view, taken along thelines A-A′ of FIG. 9A and viewed in the direction of arrow. FIGS. 10Aand 10B show a state that the flange of the plunger in the syringe isheld by the slider portion. FIG. 10A is a side view of the essentialportion of the apparatus according to the present invention, and FIG.10B is a front view, taken along the lines A-A′ of FIG. 10A and viewedin the direction of arrow.

In FIGS. 9A and 9B, if a push button 17-1 is pushed, the holding arms 27of a slider 16 for holding the flange of the plunger are rotated aroundshafts 27-1, and opened so that the slider 16 can be approached to theend of said plunger without contacting with the holding arms 27. Then,as shown in FIG. 10A, the slider 16 is moved in the leftward directionin FIG. 9A so that a contact surface 16-1 of the slider 16 is broughtinto contact with the end surface of the plunger 15. When the pushbutton 17-1 of the slider 16 is retracted, the holding arms 27 arerotated so as to engage with the flange 15-1 of the plunger as shown inFIG. 10B, and the slider 16 is approached to the flange of the plungerfor holding.

FIGS. 11A to 11C are views for explaining the essential portions of theslider 16 shown in FIGS. 9A and 9B, and FIGS. 10A and 10B. FIG. 11Ashows a state that the holding arms 27 for holding the flange of theplunger are closed. FIG. 11B shows a state that the holding arms 27 areopened. FIG. 11C shows a state that the syringe 14 and the plunger 15are held by the slider 16. In FIGS. 11A to 11C, a reference numeral 27-2denotes a screw groove on the shaft 27-1, a reference numeral 28 denotesa driving lever of the holding arm 27, 28-1 denotes a shaft for thelever 28, 28-2 denotes an engaging pin engaging with the screw groove27-2, and 29 denotes a return spring. Two holding arms 27 and partscorresponding thereto are provided so as to be rotated in the directionsopposite to each other.

In FIG. 11B, if the push button 17-1 of the releasing device (not shown)for the slider is pushed, the driving lever 28 for the holding arms 27is rotated centering around the shaft 28-1, so that the shafts 27-1 ofthe holding arms 27 are moved in the leftward direction against thereturn springs 29 because the engaging pin 28-2 is engaged with thescrew groove 27-1 on the shaft 27-1 of the holding arm 27. At the sametime, the shafts 27-1 are rotated in the counter-clockwise direction bythe action of the engaging pins 28-2 and the screw grooves 27-2, so thatthe holding arms 27 for holding the flange of the plunger are opened. Asshown in FIG. 11A, when the push button 17-1 is returned the lever 17 ofthe releasing device is returned and the driving lever 28 of the holdingarms 27 is also returned. Accordingly, the shafts 27-1 are moved in therightward direction by the action of the engaging pins 28-2 and thescrew grooved 27-2, so that the holding arms 27 are closed. In FIG. 11A,the holding arms 27 approach to a contact portion 16-2 of the plunger,because the syringe 14 is not yet mounted. FIGS. 11A and 11B show astate that the push button 17-1 is operated in the absence of thesyringe. As shown in FIG. 11C, if the push button 17-1 is returned in astate that the flange 15-1 of the plunger 15 is contacted with thecontact portion 16-2 of the slider 16, the holding arms 27 urge theflange 15-1 of the plunger to the contact portion 16-2 of the slider 16for holding. In the state shown in FIG. 11C, two holding arms 27 urgethe flange 15-1 to the contact portion 16-2 of the slider with the forceof the return spring 29 for holding, so that the flange 15-1 of theplunger can be held positively by the slider 16, ever if the thicknessof the flange 15-1 is varied.

In case that the syringe 14 is to be released from the main body 21 ofthe liquid infusion apparatus, the syringe 14 can be released easilyfrom the main body 21, because two holding arms 27 are opened when thepush button 17-1 is pushed.

According to the liquid infusion apparatus of the present inventionhaving the above construction, by pushing the push button when thesyringe is installed in the main body of the liquid infusion apparatus,the holding arms for holding the flange of the plunger are moved in themoving direction of the slider and rotated to hold the flange of theplunger easily, and by returning the push button the holding arms urgethe flange to the slider for holding. Accordingly, the flange can alwaysbe held by the slider positively even if the size of the syringe ischanged.

Another embodiment of the liquid infusion apparatus according to thepresent invention will be explained with reference to FIGS. 12A˜12C.FIGS. 12A˜12C each shows an enlarged cross section of essential portionsof the slider 16. FIG. 12A shows a state that the holding arms 27 areopened and the flange of the plunger 15 is not mounted on the slider 16.FIG. 12B shows a state that the holding arms 27 are closed. FIG. 12Cshows a state that the flange 15-1 of the plunger 15 is held by theholding arms 27. In order to avoid the complexity, the explanation ofthe driving means for the holding arms 27 is omitted.

In FIGS. 12A˜12C, a reference numeral 30 denotes a pressure sensor and31 denotes a pressure transmitting portion.

As shown in FIGS. 12A and 12B, the pressure sensor 30 is fixed to theslider 16, and a pressure receiving portion thereof is connected to thecontact portion 16-2 through the pressure transmitting portion 31. InFIGS. 12A and 12B, the holding arms 27 are not contacted with thecontact portion 16-2 of the slider, so that no pressure is applied tothe pressure sensor 30.

In FIG. 12C, the flange 15-1 of the plunger is contacted with thecontact portion 16-2 of the slider, the holding arms 27 are closed, andthe holding arms 27 urge the flange 15-1 of the plunger to the contactportion 16-2 of the slider with the force of return springs 29. In thisstate, an output corresponding to the force of the return spring 29 isgenerated from the pressure sensor 30, because the flange 15-1 of theplunger is pressed to the contact portion 16-2 by the return springs 29.

FIG. 13 is a diagram showing the relation between the pressure appliedto the pressure sensor 30 and the output thereof, and a point 1 of theordinate corresponds to zero pressure and points 2, 3, 4 eachcorresponds to each pressure of the operation states. In FIG. 13, thepoint 1 of the ordinate shows a state that the syringe is not mounted onthe slider as shown in FIGS. 12A and 12B, so that no pressure is appliedto the pressure sensor 30 and the output is zero. The point 3 of theordinate shows a state that the flange 15-1 of the plunger is contactedwith the contact portion 16-2 of the slider and pressed by the holdingarms 27 for holding as shown in FIG. 12C, so that the output of thepressure sensor corresponds to the force of the return spring 29. Inthis state, the motor 5 is inoperative and the slider 16 does not urgethe plunger 15.

When the motor 5 is rotated in a predetermined direction at apredetermined speed in the state shown in FIG. 12C, the slider 16engaged with the feed screw 7 urges the plunger 15 in the predetermineddirection at a predetermined speed to exhaust the liquid. The output ofthe pressure sensor 30 is increased to a value more than the point 3corresponding to the value of pressure required normally to exhaustliquid, so that the maximum pressure is determined as a point 4. Thepoint 2, for example, is determined between the points 3 and 1 in orderto detect the negative pressure applied to the plunger. The points 1, 2,3 and 4 shown in FIG. 13 are set in a comparison circuit (not shown) andcompared with the output of the pressure sensor 30 to generateprocessing signals corresponding to each state.

When the output of the pressure sensor 30 reaches to the point 1, asignal indicating that no syringe is set is generated. When the outputof the pressure sensor 30 reaches to a value more than the point 3, butless than the point 4, a signal indicating that the operation is normalis generated. When the output of the pressure sensor 30 reaches to avalue more than the point 4, a signal indicating the overload state isgenerated. When the output of the pressure sensor 30 reaches to a valueless than the point 2, a signal indicating that the negative pressure isapplied to the plunger is generated.

According to the liquid infusion apparatus of the present inventionhaving the above construction, by comparing the output of the pressuresensor with the values set in the comparison circuit, signals indicatingthe overload state, out of syringe state, and negative pressuregenerating state, respectively, can be generated, so that the liquidinfusion operation can be carried out safely.

Another embodiment of the liquid infusion apparatus according to thepresent invention will be explained with reference to FIGS. 14A, 14B,15A and 15B. FIG. 14A shows a side view of essential portions of a statethat the flange 15-1 of the plunger is not mounted on the slider 16.FIG. 14B shows a front view, taken along the lines A-A′ of FIG. 14A andviewed in the direction of arrow. FIG. 15A shows a side view ofessential portions of a state that the flange 15-1 of the plunger isheld by the slider. FIG. 15B is a front view, taken along the lines A-A′of FIG. 15A and viewed in the direction of arrow.

In FIGS. 14A, 14B, 15A, and 15B, two holding arms 18 of the slider 16for holding the flange of the plunger are supported by the shafts 18-1rotatably freely and urged to rotate by springs 33 in the clockwisedirection, each of said holding arms having a small projection 32 at theside face thereof. On the other hand, the lever 17 for operating aninterlocking rod 34 interlocking with the releasing device (not shown)of the slider is supported by a shaft 17-2 rotatably freely, and aprojection 17-3 is provided so as to project in the leftward directionfrom a position lower than said shaft 17-2 of the lever 17, so that whensaid push button 17-1 of the lever 18 is pushed, said arm 18 is rotatedin the counter-clockwise direction against the force of the spring 33 bythe tip end of the projection 17-3 through the small projection 32provided at the side face of the arm 27. Accordingly, the holding arms18 are opened to receive therein the flange 15-1 of the plunger easily.

As shown in FIGS. 15A and 15B, the projection 17-3 of the lever 17 isretracted, the holding arms 18 is rotated in the clockwise direction bythe force of the spring 33, and the flange 15-1 of the plunger isbrought into contact with the contact portion 16-2 of the slider 16 forholding, when the slider 16 is moved to a direction directing to the endportion of the plunger 15 of the syringe so that the contact portion16-2 of the slider 16 is brought into contact with the end of theplunger, and the push button 17-1 of the lever 17 is returned.

Specifically, the flange 15-1 of the plunger can be held positively evenif the size of the flange is varied according to the mechanicalprecision, because the flange 15-1 of the plunger is pressed to thecontact portion 16-2 of the slider 16 by the holding arms 18 with theforce of the springs 33 for holding.

In case that the syringe 14 is to be released from the main body 21 ofthe liquid infusion apparatus, the syringe 14 can be released easily,because the holding arms 18 are opened to release the flange of theplunger when the push button 17-1 of the lever 17 is pushed.

According to the above liquid infusion apparatus, the press holding andrelease of the flange can be carried out by the operation to push theslider release button when the syringe is mounted on or released fromthe main body of the liquid infusion apparatus, so that the handling isvery easy and the load of the operator becomes small.

Another embodiment of the present invention will now be explained withreference to FIGS. 16A, 16B, 17A, 17B, 18A, 18B, 19A, 19B, 20A, 20B, 21Aand 21B. FIGS. 16A and 16B show a state that a half-nut releasing deviceis engaged and a half-nut is engaged with the feed screw. FIG. 16A is aside view of essential portions of the apparatus according to thepresent invention. FIG. 16B is a cross section of the essential portion,taken along the lines A-A′ of FIG. 16A. FIGS. 17A and 17B show a statethat the half-nut is released. FIG. 17A is a side view of the essentialportion of the apparatus. FIG. 17B is a cross section of the essentialportion, taken along the lines A-A′ of FIG. 17A.

In FIGS. 16A, 16B, 17A and 17B, reference numeral 16-4 denotes anextending portion of the slider 16, reference numeral 35 denotes areturn spring for an interlocking rod 34, 36 denotes a half-nutreleasing device, 36-1 denotes a releasing cam, 37 denotes a half-nutholding portion, 37-1 denotes a half-nut sliding groove, 37-2 denotes arelease spring for the half-nut, 38 denotes a feed screw, 39 denotes ahalf-nut, and 39-1 denotes a bearing.

As shown in FIGS. 16A, 16B, 17A and 17B, the half-nut holding portion 37is provided on the extending portion 16-4 of the slider 16 extendingalong the feed screw 38 movably freely with respect to the feed screw38, and the half-nut sliding groove 37-1 extending normally to the feeddirection of the feed screw 38 is provided at the half-nut holdingportion 37. The half-nut 39 is inserted slidably into the sliding groove37-1 to support the half-nut by the feed screw detachably, and thehalf-nut releasing device 36 is fixed on the tip end of the interlockingrod 34 having the return spring 35 arranged in parallel with theextending portion 16-4. The releasing cam 36-1 having a step extendingto the forward direction of the interlocking rod 34 is formed on thehalf-nut releasing device 36 at a position facing the end portion of thehalf-nut 39, the bearing 39-1 provided at the end of the half-nut 39 isbrought into contact with the releasing cam 36-1, and the half-nut 39 isurged to a releasing direction by a spring 36-2 for releasing.

As shown in FIGS. 17A and 17B, the releasing can of the half-nutreleasing device 36 fixed to the interlocking rod 34 is moved leftwards,and the bearing 39-1 of the half-nut 39 is brought into contact with thelower step of the releasing cam 36-1, so that the half-nut 39 isseparated from the feed screw 38 by the force of the spring 36-2, whenthe push button 17-1 of the releasing lever 17 is pushed, and theinterlocking rod 34 is moved leftwards against the force of the returnspring 35.

As shown in FIGS. 16A and 16B, the interlocking rod 34 is movedrightwards, and the bearing 39-1 of the half-nut 39 is brought intocontact with the upper step of the releasing cam 36-1, so that thehalf-nut 39 is brought into engagement with the feed screw 38 againstthe force of the spring 36-2, when the push button 17-1 of the releasinglever 17 is retracted, and the interlocking rod 34 is moved rightwardsby the force of the return spring 35.

As a result, the half-nut 39 is prevented from floating from the feedscrew, because the half-nut 39 is urged in the direction normal to thefeeding direction of the feed screw by the upper step of the releasingcam.

Another embodiment of the present invention wherein both of the half-nutreleasing device 36 and the holding arm for press holding the flange ofthe plunger by the slider 16 are provided will now be explained. FIGS.18A and 18B show a state that the flange of the plunger is not yet heldby the slider 16. FIG. 18A is a sectional side view of the essentialportion. FIG. 18B is a view, taken along the lines A-A′ of FIG. 18A.FIGS. 19A and 19B show a state that the flange of the plunger is held bythe slider 16. FIG. 19A is a sectional side view of the essentialportion. FIG. 19B is a view, taken along the lines A-A′ of FIG. 19A.

In FIG. 18, the slider 16 is arranged at a position remote from theplunger 16, and when the push button 17-1 is pushed the slider releasinglever 17 is rotated around the shaft 17-2 and the projection 32 of thearm 18 is pushed by the tip end of the projection 17-3 at the left sideof the slider releasing lever 17, so that the arm 18 is rotated in thecounter-clockwise direction against the force of the return spring 33.As a result, the tip end of the arm 18 is lowered from the position ofthe flange 15-1 of the plunger so that the flange 15-1 of the plungercan be passed easily through the arms. As shown in FIG. 18B, the holdingarms 18 are positioned at the outside of the flange 15-1 of the plunger.On the other hand, the bearing 39-1 is brought into contact with thelower step of the releasing cam 36-1, and the half-nut 39 is lowered bythe force of the spring 36-2 and separated from the feed screw 38, sothat the slider can be moved freely in the moving direction of theplunger, when the interlocking rod 34 is moved in the leftward directionagainst the force of the return spring 35 by the other end of the sliderreleasing lever 17 to move the half-nut releasing device 36 connected tothe interlocking rod 34 in the leftward direction.

As shown in FIG. 19A, the projection 17-3 of the releasing lever 17 isretracted, and the holding arm 18 is rotated in the clockwise direction,so that the flange 15-1 of the plunger is pressed to the contact portion16-2 of the slider 16 and held by the tip end of the holding arm 18,when the slider 16 is moved toward the end portion of the plunger tobring the contact portion 16-2 of the slider 16 into contact with theend portion of the flange 15-1 of the plunger 15, and the push button17-1 of the releasing device of the slider is released.

On the other hand, when the interlocking rod 34 to which the other endof the slider releasing lever 17 is contacted is moved in the rightwarddirection by the force of the return spring 35, the half-nut releasingdevice 36 connected to the interlocking rod 34 Is also moved in therightward direction, so that the bearing 39-1 of the half-nut is broughtinto contact with the upper step of the releasing cam 36-1, and thehalf-nut 39 is moved upwardly against the spring 36-2 and brought intoengagement with the feed screw 38. As the upper step of the releasingcam 36-1 is formed in parallel with the feed screw, the precise feedingcan be attained, because the floating movement in the radial directionof the half-nut is prevented even if a load is applied to the feed screw38.

Another embodiment of the present invention wherein both of the half-nutreleasing device 36 and the holding arm for press holding the flange ofthe plunger are provided on the slider will be explained.

FIGS. 20A and 20B show a state that the flange of the plunger of thesyringe is not yet held by the slider 16. FIG. 20A is a side view ofessential portions. FIG. 21B is a view, taken along the lines A-A′ ofFIG. 21A.

As shown in FIGS. 20A and 20B, the slider is 16 is positioned remotefrom the flange 15-1 of the plunger of the syringe 14, and two holdingarms 27 supported by the shafts 27-1 are separated from the slider 16 bythe internal mechanism of the slider 16, rotated in the directions ofarrows and opened so that the flange 15-1 of the plunger can be broughtinto contact with the contact portion 16-2.

As shown in FIGS. 21A and 21B, two holding arms 27 supported by theshafts 27-1 approach the slider 16 and are rotated in the directions ofarrows and closed, so that the flange 15-1 of the plunger is pressed toand held by the contact portion 16-2 of the slider 16, when the slider16 is moved toward the plunger to bring the contact portion 16-2 intocontact with the flange 15-1 of the plunger, and the release button 17-1is retracted.

This mechanism is shown detailedly in FIGS. 20A, 20B, 21A and 21B. FIG.20A is a cross section of the essential portion in a state that theplunger is not yet contacted with the slider 16. FIG. 20B is a sideview, taken along the lines A-A′ of FIG. 20A. FIG. 20B shows a statethat the release button 17-1 is pushed, and the interlocking rod 34 ismoved in the leftward direction, so that the bearing 39-1 of thehalf-nut is brought into contact with the lower step of the releasingcam 36, and the half-nut 39 is lowered by the force of the spring 36-2to release the engagement of the feed screw 38. Two holding arms 27 aresupported rotatably freely by the shafts 27-1 and movably in the forwarddirection of the slider 16. A guide groove for rotation is formed at oneside of the shaft 27-1 opposite to the other side of the shaft 27-1 onwhich the holding arm 27 is mounted. The holding arm 27 is urged to theplunger contact surface of the slider by the return spring 29.

The driving lever 28 for driving the holding arm 27 supported by theshaft 17-2 is rotated in the clockwise direction when the releasingbutton 17-1 is pushed. The shaft 27-1 is moved in the leftward directionagainst the return spring 29 and rotated by the action of the guidegroove 27-2 because the engaging pin 28-2 provided at one end of thelever 28 is engaged with the guide groove 27-2 provided on the shaft27-1 of the holding arm 27, so that as shown in FIG. 20B the holdingarms 27 are opened and the flange of the plunger can be brought intocontact with the contact surface of the slider 16.

In FIGS. 20A and 20B, the releasing lever 17 is restored, and theinterlocking rod 34 is moved in the rightward direction by the force ofthe return spring 35, so that the bearing 39-1 is brought into contactwith the upper step of the releasing cam 36-1 of the half-nut releasingdevice 36, and the half-nut 39 is brought into engagement with the feedscrew 38, when the slider 16 is moved and contacted with the flange ofthe plunger, and the released button 17-1 is restored, as shown in FIGS.21A and 21B. On the other hand, when the release button 17-1 isrestored, the driving lever 28 for the holding arm 27 is rotated in thecounter-clockwise direction, the engaging pin 28-2 engaged with theguide groove 27-2 of the shaft 27-1 is moved in the rightward direction,and the holding arm 27 is rotated by the force of the spring 29, so thatthe flange is pressed to and held by the contact portion 16-2 of theslider 16. The flange of the plunger can be held positively by theslider, because the holding arm 27 is attracted toward the plungercontact surface of the slider by the force of the return spring 29 whilethe shaft 27-1 is rotated.

Further, the cross section of the tooth of the feed screw 34 is inclinedto a plane normal to the feeding direction of the screw, so that thefeed screw can be manufactured by the form rolling process etc.economically with high precision. On the contrary, the half-nut 39 maybe floated in the radial direction thereof on loading. However, theupper step of the release cam 36-1 is formed in parallel with the screw38 and urges the half-nut 39 toward the screw 38, so that the half-nut39 is prevented from floating to ensure the precise feeding. Further, ifthe cross section of the tooth of the feed screw 38 is saw tooth shapeand the vertical surface thereof is determined as the forward side, thefloating of the half-nut 39 on loading can be prevented, and the screwcan be manufactured economically and easily.

In the liquid infusion apparatus having the above construction, theengagement and disengagement of the slider with the feed screw caneasily be carried out by the operation of the slider release button, andthe flange of the plunger can be pressed to and held by the rotatableslider.

In the other embodiment of a liquid infusion apparatus shown in FIG. 22,the feed screw 7 is connected to the rotary shaft of the electric motor5 through a pinion 6-1, a one-way clutch 19 and a large gear 6-2. Assaid one-way clutch, a conventional clutch as shown in FIG. 23 can beused. The clutch comprises a cylinder 7-2 fixed coaxially to an axis 7-1of the feed screw 7, a plurality of triangular grooves 7-3 formed on theouter periphery of the cylinder 7-2, an outer cylinder 20 fixed to saidlarge gear 6-2, the inner peripheral surface of said outer cylinder 20facing the outer peripheral surface of said cylinder 7-2, and balls 20-1each inserted into a space formed between the inner peripheral surfaceof said outer cylinder 20 and said triangular groove 7-3.

In the liquid infusion apparatus shown in FIG. 22, when the electricmotor 5 is rotated in the predetermined direction (in the clockwisedirection, for example), the feed screw 7 is rotated by the electricmotor 5 through the one-way clutch 19, so that the slider 16 is urged tomove the plunger 15 in the liquid exhausting direction and thus theliquid infusion apparatus is operated correctly. The one-way clutch 19slips and the rotation of the electric motor 5 is not transmitted to thefeed screw 7, if the electric motor 5 is rotated reversely(counter-clockwise direction) for some reason, and accordingly such awrong operation that the plunger 15 is moved reversely (suctiondirection) by the slider can be prevented.

The above liquid infusion apparatus has such an excellent function thatthe wrong operation, such as the reverse moving of the plunger can beprevented even if the electric motor is rotated reversely due to theelectric noises or the like.

INDUSTRIAL APPLICABILITY

As stated above, the liquid infusion apparatus of the present inventionis useful for the oscillating device of the plunger of the syringe.

The scope of the present invention should not be limited to the aboveembodiments and should be defined by the terms of the claims appendedhereto.

What is claimed is:
 1. In a liquid infusion apparatus having a feedscrew driven by a prime mover and a slider movable linearly and engagedwith said feed screw so as to push a plunger of a syringe for exhaustingliquid in the syringe, the improvement characterized by comprising aholding arm for pushing a flange of said plunger in a direction reverseto a pushing direction of the plunger toward a plunger holding portionof said slider for holding, a pressure sensor provided at said plungerholding portion of the slider, and a processing circuit for comparing anoutput of said pressure sensor with a plurality of reference values togenerate a processing signal.
 2. The liquid infusion apparatus of claim1, wherein said plural reference values comprise: a first valuecorresponding to an output of said pressure sensor in a state that theflange of the plunger is held by the plunger holding portion of theslider; and a second value corresponding to an output of said pressuresensor at the maximum desired pressure within the syringe.
 3. The liquidinfusion apparatus of claim 1, wherein said plural reference valuescomprise: a first value corresponding to an output of said pressuresensor in a state that the flange of the plunger is held by the plungerholding portion of the slider; and a second value corresponding to anoutput of said pressure sensor at the maximum desired pressure withinthe syringe; wherein said reference values comprise means forgenerating: (1) a signal indicating a state that no syringe is set whenthe output of the pressure sensor is less than said first value; (2) asignal indicating a normal state when the output of the pressure sensoris between said first and second reference values; and (3) a signalindicating an overload state when the output of the pressure sensor isgreater than said second reference value.
 4. The liquid infusionapparatus of claim 1, wherein said plural reference values comprise: afirst value corresponding to an output of said pressure sensor in astate that the flange of the plunger is not yet held by the plungerholding portion of the slider; a second value corresponding to an outputof said pressure sensor in a state that the flange of the plunger isheld by the plunger holding portion of the slider; and a third valuecorresponding to an output of said pressure sensor at the maximumdesired pressure within the syringe.
 5. The liquid infusion apparatus ofclaim 1, wherein said plural reference values comprise: a first valuecorresponding to an output of said pressure sensor in a state that theflange of the plunger is not yet held by the plunger holding portion ofthe slider; a second value corresponding to an output of said pressuresensor in a state that the flange of the plunger is held by the plungerholding portion of the slider; and a third value corresponding to themaximum desired pressure within the syringe; wherein said referencevalues comprise means for generating: (1) a signal indicating a statethat no syringe is set when the output of the pressure sensor is lessthan said first value; (2) a signal indicating a vacuum state within thesyringe when the output of the pressure sensor is between said first andsecond reference values (3) a signal indicating a normal state when theoutput of the pressure sensor is between said second and third referencevalues; and (4) a signal indicating an overload state when the output ofthe pressure sensor is greater than said third reference value.
 6. In aliquid infusion apparatus having a feed screw driven by a prime moverand a slider movable linearly and engaged with said feed screw so as topush a plunger of a syringe for exhausting liquid in the syringe, theimprovement characterized by comprising a holding arm for pushing aflange of said plunger in a direction reverse to a pushing direction ofthe plunger toward a plunger holding portion of said slider for holding,a pressure sensor provided at said plunger holding portion of theslider, and a processing circuit for comparing an output of saidpressure sensor with a plurality of reference values to generate aprocessing signal; wherein said plural reference values are 1, 2, 3 and4, and set in a processing circuit for comparing, the value 1corresponding to an output of said pressure sensor in a state that theflange of the plunger is not yet held by the plunger holding portion ofthe slider, the value 3 corresponding to an output of said pressuresensor in a state that the flange of the plunger is held by the plungerholding portion of the slider, which is more than the output of thevalue 1, the value 4 corresponding to the maximum output of saidpressure sensor, which is more than the output of the value 3, and thevalue 2 corresponding to an output of said pressure sensor which is morethan the output of the value 1, but less than the output of the value 3,respectively, and further comprising means for generating (1) a signalindicating a state that no syringe is set when the output of thepressure sensor becomes to the value 1, (2) a signal indicating a normalstate when the output of the pressure sensor becomes to a value morethan the value 3, but less than the value 4, (3) a signal indicating anoverload state when the output of the pressure sensor becomes to a valuemore than the value 4, and (4) a signal indicating a case that anegative pressure is applied on the plunger when the output of thepressure sensor becomes to the value 2, respectively.
 7. In a liquidinfusion apparatus having a feed screw driven by a prime mover and aslider movable linearly, which is engaged with said feed screw so as topush a plunger of a syringe for exhausting liquid in the syringe, theimprovement characterized by comprising a holding means for holding aflange of said plunger by the slider, which is fixed to a supportingshaft movable in a moving direction of the slider and supportedrotatably freely, wherein said supporting shaft is rotated so as toseparate said holding means from said flange when said holding means ismoved so as to go away from the slider, and said supporting shaft isrotated so as to bring the holding means into engagement with saidflange when said holding means is approached to the slider.
 8. Theliquid infusion apparatus according to claim 7, wherein said holdingmeans is capable of positive engagement with flanges of variedthickness.
 9. In a liquid infusion apparatus having a feed screw drivenby a prime mover and a slider movable linearly, which is engaged withsaid feed screw so as to push a plunger of a syringe for exhaustingliquid in the syringe, the improvement characterized by comprising alever supported rotatably freely by a first shaft arranged horizontallyand normally to a moving direction of said slider, a push buttonprovided at one end of said lever so as to project from said slider, aslider releasing device, an interlocking rod interlocking with saidslider releasing device, the other end of said lever being contactedwith said interlocking rod, holding means supported by said sliderrotatably by a second shaft for press holding the flange of the plungerby the slider, a spring for urging the holding means to rotate in theclockwise direction, and interlocking means for interlocking saidholding means with said lever.
 10. The liquid infusion apparatus asclaimed in claim 9, wherein said interlocking means has a spring forurging said holding means to rotate in the clockwise direction.
 11. Theliquid infusion apparatus according to claim 9, wherein said holdingmeans releases said flange upon operation of said push button.
 12. In aliquid infusion apparatus having a feed screw driven by a prime moverand a slider movable linearly, which is engaged with said feed screw soas to push a plunger of a syringe for exhausting liquid in the syringe,the improvement characterized by comprising a lever supported rotatablyfreely by a first shaft arranged horizontally and normally to a movingdirection of said slider, a push button provided at one end of saidlever so as to project from said slider, a slider releasing device, aninterlocking rod interlocking with said slider releasing device, theother end of said lever being contacted with said interlocking rod,holding means supported by said slider rotatably by a second shaft,which is in parallel to said first shaft for press holding the flange ofthe plunger by the slider, a spring for urging the holding means torotate in the clockwise direction, and interlocking means forinterlocking said holding means with said lever; wherein saidinterlocking means has a projection provided on the other side of saidlever which is brought into engagement with a small projection providedon an end of said holding arm, so that said holding arm is rotated inthe counter-clockwise direction by said projection.
 13. In a liquidinfusion apparatus having a feed screw driven by a prime mover and aslider movable linearly, which is engaged with said feed screw so as topush a plunger of a syringe for exhausting liquid in the syringe, theimprovement characterized by comprising first means consisting of areleasing lever supported rotatably freely by a first shaft of theslider, a push button provided at one end of said releasing lever so asto project from said slider, a half-nut releasing device engaging withthe feed screw, a pressing portion provided at the other end of thereleasing lever for pressing an end of an interlocking rod extending inparallel with the feed screw, and a first spring for restoring saidinterlocking rod; and second means consisting of a half-nut holdingportion movable freely with respect to the feed screw, which is providedan extending portion extending in parallel with the interlocking rod andconnected as a unit to said slider, a half-nut sliding groove extendingnormal to the forward direction of the feed screw, formed on thehalf-nut holding portion, a half-nut inserted slidably into said slidinggrove and supported detachably from the feed screw, and a half-nutreleasing device fixed to the other end of said interlocking rod;wherein said half-nut releasing device has a releasing cam having at aposition facing a surface opposite to a screw surface of the half-nut astep portion in the forward direction of the interlocking rod, and asecond spring provided on the half-nut holding portion for urging in thereleasing direction the half-nut.
 14. The liquid infusion apparatus asclaimed in claim 13, further comprising a holding arm supportedrotatably freely by a second shaft, which is in parallel with said firstshaft for press holding a flange of the plunger by the slider, a thirdspring for urging the holding arm to rotate in the clockwise direction,and a projection on said releasing lever, which is brought intoengagement with a small projection provided on an end of said holdingarm.
 15. The liquid infusion apparatus as claimed in claim 13, furthercomprising a holding arm supported rotatably freely and movably in theslider moving direction by a supporting shaft for holding a flange of aplunger by the slider, wherein said supporting shaft is rotated so as toseparate said holding arm from said flange when said holding arm ismoved so as to go away from the slider interlocking with said releasinglever, and said supporting shaft is rotated so as to bring the holdingarm into engagement with said flange when said holding arm is approachedto the slider.
 16. The liquid infusion apparatus as claimed in claim 13,wherein the cross section of the tooth of the feed screw is inclined toa plane normal to the feeding direction of the feed screw.
 17. Theliquid infusion apparatus as claimed in claim 13, wherein the crosssection of the tooth of the feed screw is saw tooth shape.
 18. In aliquid infusion apparatus having a feed screw driven by a prime moverand a slider movable linearly, which is engaged with said feed screw soas to push a plunger of a syringe for exhausting liquid in the syringe,the improvement characterized by comprising means for transmitting adriving force from the prime mover only in a syringe pushing directioninserted between the feed screw and the prime mover.
 19. The liquidinfusion apparatus as claimed in claim 18, wherein said means fortransmitting the driving force is a one-way clutch.